(a) Field of the Invention
The present invention relates to a catalytic cracking catalyst composition useful for the catalytic cracking of heavy oils, and also to a catalytic cracking catalyst and a method of catalytically cracking heavy oils by using the catalytic cracking catalyst.
(b) Description of the Related Art
As crude oils are becoming heavier and the demand for gasoline and light fuel oils is increasing, the catalytic cracking of heavy oils is acquiring greater importance. In these circumstances, there is a demand for new catalytic cracking catalysts, which can crack heavy oils, such as desulfurized heavy oils, and give increased yields of gasoline and LCO fractions (light fuel fractions).
Cracking heavy oils, such as desulfurized heavy oils, into LCO fractions (light fuel fractions) or gasoline fractions requires rough cracking in macro pores (large pores) followed by more efficient cracking in meso pores (medium pores: 40-400 .ANG.).
When a catalyst poor in meso pores is used, heavy oil fractions resulting from the primary cracking cannot penetrate into the area abounding cracking active sites, but stay in macro pores for a long time to form large amounts of coke and gas, failing to use the catalyst effectively. Increasing meso pores (medium pores: 40-400 .ANG.), therefore, is required to crack efficiently the heavy oil fractions resulting from the primary cracking.
A means of increasing meso pores is the use of silica. Silica improves the diffusion of heavy oils, but hardly effects cracking into LCO and gasoline owing to the scarcity of cracking active sites. Another means is the use of silica alumina. Using silica.alumina alone, however, causes excessive cracking of heavy oils, increase the yields of gas and coke owing to a large quantity of strongly acidic cracking active sites. To produce LCO and FCC gasoline, it is therefore necessary to control meso pores and prevent excessive cracking by adding alumina, which is a relatively weak acid.
Japanese Patent Application Examined Publication No. 63-36291 (1988) discloses a hydrocarbon cracking composition containing spray-dried .omega. alumina. It, however, is unsuitable for the production of LCO and gasoline from heavy oils, such as desulfurized heavy oils because the objective pores are not meso pores but macro pores of 1000-3000 .ANG., and .chi. alumina is not a boehmite gel alumina.
Japanese Patent Application Unexamined Publication No. 2-277548 (1990) discloses a catalytic cracking catalyst containing bayerite and/or .eta. alumina, but does not mention meso pores. Further, bayerite and .eta. alumina transfer to .theta. alumina having a decreased surface area at high temperatures in the regenerators of residual oil fluidized catalytic cracking apparatuses for treating heavy oils, such as desulfurized heavy oils, to decrease the yields of LCO and gasoline fractions.